"Marble Blast was unable to find a compatible dislpay driver! Check with you video card vendor to see if updated device drivers are available." [yes, I spelled display wrong. It's like that in the error message]
It was working perfectly find yesterday. I did switch to OpenGL, but that was fine too. [Direct3D was lagging.]
Can someone tell me how to fix this?
For future reference, the current MBP version is MBP 1.50 RC1, not Beta 3. If you are indeed running Beta 3, and not running the RC1 version, then download it from the site from the Downloads menu. If you are using the launcher that opens a rather plain white and text window, then you have RC1.
I've stopped using fullscreen because I found that when MBG/P or whatever mod crashes, the system doesn't handle it very gracefully, and nothing gets cleaned up and shutdown after the game crash. There's a certain amount of raw control that the game acquires in fullscreen mode. Windowed mode to your screen resolution or a resolution slightly smaller for MBG/P works just fine. I'd recommend it because it's easier to get out of messy (and buggy) situations.
Third, just change the fullscreen value above to 0 in mbpPrefs.cs and delete any existing mbpPrefs.cs.dso file, as the game would read that instead.